It is known to provide, for example in a machine or mechanism for unrolling webs of material from rolls, a roll carrier rotatable about a roll axis for a delivery roll from which a web is drawn, and a roll carrier rotatable about an axis parallel to that of the roll carrier for receiving a new roll from which a web is to be subsequently drawn.
Each of the roll carriers is adjustable in the direction of the roll axis and for positioning in this direction can be provided with a respective servomechanism or positioning drive.
The positioning drives for the roll carriers of each roll in the position of a delivery roll are generally each provided with a sensor which monitors the position of the edge of the delivered web of material and provides an actual value or instantaneous value signal to the controller for that positioning drive.
In unwinding or paying out rolls of web material, it is known to control the position of the edges of the unrolling or delivered web, to detect position changes in the longitudinal edges of the web and to use the position deviation to adjust the positioning drive (see the German commercial bulletin DR 7201 "FREMATIC--Kantenregelungen" of Fa. Frede--Automatic KG, Dusseldorf, Germany, VDI-Nachrichten 02.05.62 Page 6, ETZ-B, Vol. 12, No. 18, 05.09.69, Page 447).
Control devices of the aforedescribed type are known in roll changers as well, in which the web-edge sensor is provided in combination with the controller and positioning drive for each roll as it becomes the payout or delivery roll to control the edge position of the delivery web. The new roll, in such cases, is found in a waiting position which enables the connection of the controller edge of the web of the delivery roll with the leading end of the web of the new roll.
The new roll, as well, can be axially prepositioned in its waiting position with the aid of the positioning drive of its roll carrier to minimize any time delay between connection of the new roll to the trailing end of the previously delivered web and to ensure that the longitudinal edges of both webs are as flush as possible with one another.
This prepositioning has been found to ensure a rather exact disposition of the outer edges of the innermost turns of the new roll with the longitudinal edges of the delivered web. Problems are encountered, however, when the turns of the new roll are offset from one another so that the outer turns are axially shifted relative to the inner turns either as a result of winding errors in the production of the roll or as a result of roll deformation during transport, storage, handling or the like.
Such axial deviations of the outer web turns with respect to the inner web turns are not noted by conventional control devices and result in a corresponding lateral shift when the trailing end of the delivered web is to be connected to the leading end of the new roll when its laterally offset outer web turns.